Since 1976 this project has emphasized dysregulation of the hypothalamo-pituitary-adrenal (HPA) neuroendocrine system in patients with melancholia or biological depression. The main focus was the dexamethasone suppression test (DST) - as a diagnostic aid, its association with other biological markers, its clinical correlates and its implications for a new nosology of clinical depressions. We have now shifted our emphasis to basic studies of HPA physiology and pathophysiology in normal humans and depressed patients. With our new, highly sensitive and specific assay for ACTH, we are studying the dynamic regulation of pituitary ACTH release by corticotropin releasing factor (CRF) and vasopressin under conditions of low glucocorticoid feedback (with RU 486) and high glucocorticoid feedback (with dexamethasone). The experiments are designed to clarify the functional status of ACTH-secreting anterior pituitary cells in depressed patients with abnormal DSTs and disinhibited HPA activity. The pituitary sensitivity to CRF and/or vasopressin under high and low feedback conditions will yield data relevant to the hypothesis of excessive CRF release through hypothalamic-limbic overdrive in depression. Other experiments will use gas chromatographic-mass spectrometric methods to study dexamethasone metabolism, single-dose pharmacokinetics, profile of metabolites, and immuno-cross-reactivity of metabolites in clinical radio- immunoassays for plasma dexamethasone. These studies will advance our understanding of normal HPA regulation and the pathophysiology of this system in depression. The results will lead to improved HPA assessment procedures, will suggest new approaches to the biological classification of depressions, and will likely suggest revisions of current concepts of the psychobiology of stress.